Half-Baked Meaning

(idiomatic, informal, frequently derisive) Incomplete; (of an idea or scheme) not fully planned or carefully considered, ill-conceived, unsound or badly thought-out; (of a person) foolish or having no common sense.

Example: Used other than as an idiom: Partially cooked by heating in an oven.
  When the casserole is half-baked, take it out and sprinkle the grated cheese on top.
  The guy had some half-baked idea for getting rich in the stock market.
1960, P. G. Wodehouse, Jeeves in the Offing, chapter XVII:
  She came skipping to me just now, clapping her little hands and bleating about how very, very happy she was, dear Mrs Travers. The silly young geezer. I nearly conked her one with my trowel. I'd always thought her half-baked, but now I think they didn't even put her in the oven.